A conventional tubular door lock has an inner knob provided with a turning button, which is rotated to lock the lock from inside. So, when the lock in locked condition is to be unlocked, at first the turning button has to be rotated back and then the inner knob can be rotated to open the door. In emergency, the lock can delay a person attempting to escape from a room or a house in opening the door equipped with it.
Some tubular door locks used in a rest room are improved to have a press button instead of a turning button in the inner knob, which is more convenient to open the door. But for little children or feeble persons, it is still somewhat unsafe, because the lock once locked needs a little force to rotate the inner knob to unlock it, while it is rather easy to press down the press button to lock it from inside.